So basically you are asking what we think is better for the 'RP atmosphere' in IC-channels - empty or half-filled with lurkers.
I think I'd have to go with empty, or only the active ones at that. If there are 5 guys in a channel and onle two of them are even there, it sometiems feels a bit bothersome to engage in what is essentially a conversation between two people. These are usually private - in the way that, no-one else can hear/see them, but with 3 other guys that potentially logg the chat, they have full access to what you have been saying.
Minor issue, after all if you wanted it totally private that's what convos are for. What's worse is the way these other toons get back to being active and then possibly join the chat. Say your in a 'bar' channel - two of you are having a drink and a chat. The rest of the bar is empty. Then another guy get's on and enters '/me enters bar and looks around' and all that. This is an excuse for your two toons to notice the arrival of this third guy and greet said guy upon arrival. If you arrive and there is one afk guy there, it's more '/me enters and waves to X' followed by a half-hour delay until the other guy returns to go 'oh, hi Y, I didin't notice you/were half asleep/were tripping on my blue pillz, sorry, hor are you?'
Awkward. Now you have to somehow find something that justifies sitting around for hours effectively not doing a thing. Better perhaps, if you don't afk around in IC channels at all, though I can only see this issue with 'bar' locations and such. After all, 'merely' IC intel channels, or public coms channels or whatever isn't that bad - it's just a coms channel after all, not a location of note.